Various moisturizers have been mixed with agents for external use on skin such as cosmetics in the related art. As typical moisturizers, hyaluronic acid, pyrrolidone carboxylate, glycerin, and the like are widely used. Although these have a high moisturizing effect, if a large amount of the moisturizer is mixed in to improve the effect, a feeling of stickiness to the skin becomes strong, which results in undesirable feeling during use in some cases. It is known that mixing oil together with a moisturizer is effective for suppressing the feeling of sliding and feeling of stickiness of the moisturizer. Moreover, an attempt at using a specific copolymer, a polyoxyethylene derivative, and a water-soluble polymer concurrently with a moisturizer is being made.
In order to relieve the feeling of stickiness of a moisturizer, a method of mixing in a polyoxyethylene polyoxypropylene copolymer and polyethylene glycol dialkyl ether has been reported (PTLS 1 and 2). However, with the components disclosed in these patent literature documents, an emulsion stabilizing effect for oil is not expected. Consequently, many restrictions are imposed on formulation, and the effect of suppressing stickiness is limited.
PTL 3 reports a method of reducing the feeling of stickiness of a moisturizer by mixing in native gellan gum. However, since the native gellan gum forms a hard and brittle gel, the moisturizer is not evenly spread when being applied to the skin, which leads to a defect that uniform coating is difficult.
Various types of water-soluble ionic substances are mixed into cosmetics in many cases. Examples of the water-soluble ionic substances include ascorbic acid derivatives as whitening components or as other active ingredients, pH adjustors and sequestering agents for preventing alteration of cosmetics or for maintaining usability of cosmetics, and the like.
However, since the gel strength of the native gellan gum changes in the presence of water-soluble ionic substances, mixing in of these components is restricted in terms of formulation.
When agents for external use on skin including cosmetics are applied, the agents are spread on the skin by using fingers. If the agent for external use on skin attached to the fingers used for the application absorbs moisture, the components mixed into the agent for external use on skin exhibit a lubricating property, even once the agent has dried. Accordingly, when delicate work such as gripping a pen, closing the cap of a container, and picking up small objects are carried out after the application of the agent for external use on skin, the lubricating property hinders this work in some cases. Therefore, it is desired to develop a composition for external use on skin that prevents fingers used for application from easily becoming slippery even when the fingers come into contact with moisture again.
In addition, an oil-in-water type emulsion composition such as an emulsion or a cream has been widely used as cosmetics in the related art. Particularly, for cosmetics, silicone oil or oil having a high polarity is widely used as an oil which is pleasing to the sense of touch. However, since these oils are not easily emulsified, it is difficult to realize stabilization of an emulsion dispersion.
In order to keep the emulsion dispersion of oil stable, it is indispensable to add a surfactant. However, in recent years, higher safety has been required for cosmetics, so mixing a surfactant has become a problem in some cases. Particularly, for agents for external use applied to the skin, the amount of the surfactant added is desired to be small in terms of safety. However, it is difficult to reduce the amount of the surfactant added while also stabilizing the emulsion dispersion.
Generally, for emulsifying and stabilizing oil, a thickener represented by a carboxyvinyl polymer or xanthan gum is effective. Accordingly, for example, PTL 4 discloses a method of using an alkyl-modified carboxyvinyl polymer as an emulsifier, as a method of preparing an oil-in-water type emulsion cosmetic excellent in long term stability without using a surfactant. However, these thickeners are not preferable since they produce the dirt-like scum during massage when applied to the skin.
In addition, the carboxyvinyl polymer has a problem in that the viscosity is dramatically reduced in the presence of a water-soluble ionic substance such as an ascorbic acid derivative, so the stability deteriorates in some cases. Particularly, the alkyl-modified carboxyvinyl polymer has low halotolerance, which leads to a problem that this polymer cannot be mixed with a vitamin C derivative or other salt. Furthermore, though the xanthan gum shows small change in physical properties with respect to water-soluble ionic substances, nevertheless the feeling of sliminess or stickiness unique to the xanthan gum is not preferred. In addition, the xanthan gum has a defect in that the sense of touch is greatly worsened when the xanthan gum is mixed in, in a sufficient amount for securing stability.
PTL 5 discloses, as an oil-in-water type cosmetic with improved stability and halotolerance, a fluid gel (gel having fluidity) cosmetic that contains one or two or more kinds among agar, carrageenan, gellan gum, and sodium alginate as a main fluid gel agent, and contains one or two or more kinds among native gellan gum, xanthan gum, guar gum, locust bean gum, a carboxyvinyl polymer, an acrylic acid-alkyl methacrylate copolymer, hydroxyethyl cellulose, and hydroxypropyl cellulose as an agent for improving usability and stability. This fluid gel cosmetic is characterized by having an even and smooth fine gel-dispersed structure. However, this cosmetic has a problem in that a water-soluble gelation agent having disintegrating properties, such as heated and dissolved gellan gum or agar cannot be produced by stirring and cooling used in the related art but has to be produced while breaking the formed gel by means of applying a high shearing force during cooling.
PTLS 6 and 7 report low-strength agar and how to use this agar. Though a property of producing a liquid residue, which is an original property of agar, is improved to some degree in the documents, the improvement does not satisfy stability required for agents for external use on skin such as cosmetics. Moreover, the agar has a problem of producing the dirt-like scum during massage and is ineffective for stabilizing an emulsion dispersion of silicone oil or high-polarity oil which is not easily emulsified. Therefore, it is desired to develop a composition for external use on skin that improves the property of producing a liquid residue, which is an original property of agar, and does not produce the dirt-like scum.
Oil-in-water type emulsion compositions containing pigments are being used as emulsion cosmetics such as sunscreen cosmetics and a liquid foundation. As a method of stably dispersing pigments in the oil-in-water type emulsion composition, a method of using various surfactants, a method of using water-soluble polymers, and the like are being examined. However, in the method of using various surfactants, deterioration of makeup sustainability and stickiness caused by the decrease in water resistance and oil resistance is an issue. In addition, in the method of using water-soluble polymers, depending on the type of water-soluble polymers, the polymers are aggregated when being concurrently used with pigments in some cases. Furthermore, if water-soluble polymers are mixed in until a desired viscosity is obtained, problems in sense of touch such as stickiness and feeling of a film arise, and change with temperature variation becomes large, which leads to a defect that the stabilized form of a product cannot be easily maintained.
Powders such as pigments used for cosmetics are divided into hydrophilic powder and hydrophobic powder. In order to impart water resistance and water repellency to cosmetics, powder having undergone hydrophobizing treatment is used. However, since hydrophobic powder has low affinity with water in general, it is very difficult to evenly disperse hydrophobic powder in the oil-in-water type emulsion composition. As a method of stably dispersing the hydrophobic powder in the oil-in-water type emulsion composition, a method using a water-soluble solidifying agent such as agar or gelatin and a water-soluble adhesive such as methyl cellulose or xanthan gum has been reported (for example, see PTL 8). However, since general agar has a high molecular weight and forms a very strong network, spreadability of the obtained oil-in-water type emulsion composition is poor at the time of application in some cases. Consequently, it is desired to develop a pigment dispersion composition that can be stably dispersed regardless of the type of pigment, spreads excellently on the skin, is excellently pleasing to the sense of touch, and is highly safe for the skin.
Meanwhile, cleaning agents containing a surfactant as a main agent need to be thickened to an appropriate degree in some cases, in consideration of usability for a user and dispersion stability of insoluble solids contained. Examples of thickening methods used in the related art include three methods such as a method of increasing viscosity by forming a complex by means of mixing in different types of surfactants (for example, amphoteric and anionic surfactants), a method of increasing viscosity by micelle aggregation by adding an inorganic salt, and a method of using a thickener.
In a case of the method of using a combination of different types of surfactants, the amount of the surfactants contained tends to be increased. Furthermore, depending on the type of the surfactant used as a main agent, it is very difficult to increase viscosity in some cases. Examples thereof include cleaning agent compositions containing disodium polyoxyethylene lauryl sulfosuccinate, cocoyl-L-glutamic acid monotriethanolamine, polyoxyethylene lauryl ether sodium acetate, cocamidopropyl betaine, and the like as main agents. Many of these surfactants having a poor thickening property and a mixture thereof are generally considered to be hypoallergenic, so these can be expected to be used for various uses. However, even if other surfactants are combined with these surfactants, a desired viscosity is not easily achieved in many cases.
In the method of increasing viscosity by mixing in an inorganic salt, sodium chloride, sodium sulfate, or the like is mainly used as the inorganic salt. However, the thickening effect of these inorganic salts is low for the amount of the salts added, and in order to adjust the viscosity to a desired degree, a large amount of the inorganic salts need to be added, which leads to a problem in safety such as cause a sensation of irritation.
In the method of increasing viscosity by using a thickener, nonionic surfactants or polymeric thickeners are widely used. As the nonionic surfactants, polyoxyethylene alkyl ether, coconut oil fatty acid diethanolamide, polyethylene glycol distearic acid ester, and the like are used. However, these nonionic surfactants have problems in that they need to be added in a large amount, are not pleasant to the sense of touch when used, have poor low-temperature stability and poor solubility, and the like.
On the other hand, as the polymeric thickeners, hydroxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, cationized cellulose, polyvinyl alcohol, sodium polyacrylate, starch, xanthan gum, and the like are used. In the method of using the polymeric thickeners, it is possible to obtain a viscous cleaning agent composition with a relatively low level of the thickeners, and the thickeners can be easily added to hypoallergenic cleaning agent compositions highly safe for the skin. However, in cleaning agents containing the polymeric thickener concurrently with a water-soluble ionic substance, the thickening effect is diminished in many cases.
The xanthan gum has the thickening effect even in the presence of water-soluble ionic substances, and can thicken hypoallergenic cleaning agent compositions that are considered not to be easily thickened. However, the xanthan gum has defects in that its characteristic feeling of sliminess is not preferred and that its sense of touch greatly deteriorates when the xanthan gum is mixed in, in a sufficient amount to secure stability.
Cleaning agents used for cleaning skin, such as a shampoo and a cleansing agent, are required to be highly safe for the skin. Among these, cleaning agents for babies or pets are desired to be safe even being swallowed, since there is a possibility that babies or pets may accidently swallow the cleaning agents when the agents are used. Therefore, it is desired to develop a cleaning composition that is excellent in safety, is excellently pleasing to the sense of touch when used, is hypoallergenic, and has a necessary viscosity.
Against the above-described background, it is desired to develop a composition for external use on skin that can be evenly spread on the skin, does not produce a liquid residue as a result of temperature change, can reduce the feeling of sliminess of xanthan gum, and can stably contain various other components.